Turbine disc

ABSTRACT

This disclosure is directed to turbine machinery discs having improved elevation and contouring of the disc rim lugs and blade attachment slots local to the outer diameter blade attachment lug and slot surfaces of said discs thus providing a strainconforming and restraining surface for redistributing and resisting the transmission of blade shank tang stresses and strains as they develop in the root attachment lands and transition zones of the turbomachinery blades.

United States Patent [1 1 Norbut June 24, 11975 1 TURBINE DISC [76]Inventor: Theodore J. Norbut, 3 141 Claydor Dr., Dayton, Ohio 45431 [22]Filed: Mar. 25, 1974 [21] Appl. No.: 454,372

[52] US. Cl. 416/219; 416/241; 416/244; 416/248 [51] Int. Cl. FOld 5/30[58] Field of Search 416/219, 244, 248, 241 B, 416/214 [5 ReferencesCited UNITED STATES PATENTS 3,294,364 12/1966 Stanley 416/219 3,612,71810/1971 Palfreyman et a1 416/193 X 3,809,495 5/1974 Stahl 416/24 BFOREIGN PATENTS OR APPLICATIONS 920,641 11/1954 Germany 416/500 UnitedKingdom 416/241 B U.S,S.R 416/219 Primary Examiner-Everette A. Powell,Jr. Attorney, Agent, or Firm-Joseph Patrick Burke 5 7] ABSTRACT Thisdisclosure is directed to turbine machinery discs having improvedelevation and contouring of the disc rim lugs and blade attachment slotslocal to the outer diameter blade attachment lug and slot surfaces ofsaid discs thus providing a strain-conforming and re straining surfacefor redistributing and resisting the transmission of blade shank tangstresses and strains as they develop in the root attachment lands andtransition zones of the turbomachinery blades.

11 Claims, 14 Drawing Figures TURBINE DISC This invention is directed toimproved discs with rims having blade attachment slots and lugs withsmoothly radiused raised outer rim lug surfaces adjacent the rim slotsto mitigate or reduce the generation of severe stress-strainconcentrations and non-uniform load distributions in turbomachineryblading. According to this invention, these disc rims, suitable for usein turbomachinery attachment devices, exhibit restraining surfacesdifferent from prior art rims in that they afford additional restrainingsurfaces due to the elevated rim lug height at the uppermost portions ofthe rim lugs thereby providing additional, smooth contacting lugsurfaces for absorbing and distributing stresses, such as, centrifugal,centrifugal untwist, gas bending, vibratory, foreign object impact andother forms of complex stresses.

This integral disc of this invention is characterized by the followingcomposite features:

1. The outer portions of the disc rim lugs are raised (elevated)adjacent to the slots in contrast with lower disc rim portions betweensaid raised lugs.

2. These raised portions have a gradual radius of curvature, which issubstantially equal and symmetrical for each rim lug set accommodatingeach blade.

3. The curvature of the outer rim lugs is more gradual than that of thelower ends of the rim slots which accommodate the blade tang portions.

4. Each symmetrical rim slot, accommodating each peripherally mountedblade, has a pair of extended (raised) lug portions, the height(diameter) of which approximately equals that of each other.

5. Each disc rim has symmetrical approximately equal respective lowerintermediate portions (between the raised lugs), said lower portionsbeing of approximately equal diameter.

6. There is no direct sharing of tension or compres sion forces betweenadjacent blades.

In the drawings, the features of the invention are contrasted withtypical prior art configurations.

FIG. I of the drawing is a perspective view, partly in section,illustrating an individual turbine blade in its individual discattachment. It will be realized that actual turbine rotors have aplurality of such blades and disc attachments customarily spacedperipherally about the rim portion of a disc for rotation. These bladesare arranged circumferentially in fluid flow machines such, for example,as turbomachinery compressors and turbines.

FIGS. 2 and 3 are likewise perspective views, partly in section, showingfurther configurations of prior art devices evidencing similar disc rimand blade root attachment relationships.

FIGS. 4(A) and 4(8) are both side views showing a characteristic priorart disc rim having a plurality of rim slot and lug portions inchristmas tree arrangement.

FIG. 5 is a sectional view taken along the line 55 of FIG. 4( B)illustrating in detail the dead rim, live rim, web and bore portions ofsuch a disc rim.

FIGS. 6 and 7 are perspective views, partly in section, illustrating thedisc rims of this invention resulting in the improved features whichwill be pointed out hereinafter.

FIG. 8(A) is a schematic showing of a typical positioning of a prior artturbine blade in relation to the characteristic root attachments,surfacing and disc rim attachment configuration typical of FIGS. 1, 2and 3.

FIG. 8(B) is a schematic view of the blade attachment of FIG. 8(A) inperspective showing the blade attachment land surface 5.

FIG. 9 is a diagrammatic view vectorially illustrating the straindistribution typically occurring on the blade root attachment tang,adjoining blade shank and transition surfaces resulting from steadycentrifugal body forces during rotation of turbine blades mounted inprior art rims. A high strain gradient results at this point where thelocal tensile and compressive strains become additive and reinforce eachother. The strain field is entirely tensile above the point of contactand changes to compression as the load is introduced into the disc lugat the zone of contact.

FIG. 10 is a similar diagrammatic view showing in section the strainfield amplification to which prior art devices are subjected when abending moment is applied in conjunction with centrifugal body forces.Such bending moments are characteristically introduced by such causes assteady and unsteady gas dynamic pressure forces, airfoil untwist,natural resonance vibrations and instantaneous impacts from foreignobject debris.

FIGS. 11 and 12 diagrammatically illustrate by vectorial notation theeffect of the devices of the invention in providing a reduction in themagnitude of the peak strains through redistribution.

Referring to the drawings, and more particularly to FIGS. 1 and 8(8),turbine blade 1 has a platform portion 2. Beneath the blade platform isa centrally located blade shank 3 which merges into a root attachmenttransition zone shown at 4 and thence downwardly to the root attachmentland surfaces, viz., such as at surfaces 5, FIG. 8(B), of the blade tangportions 6. The blade root attachment is thus made up of blade shankportion 3 and tang portions 6 which underlie transition zone 4.

The blade root attachment is received in the cavities or slot portions 9of disc rim portions 7 of disc 8. See FIGS. 4(A) and 4(8). The mountingdisc 8 has a disc rim portion 7 in which there are a plurality ofcircumferentially located slots 9, of varying configurations dependingon blade configuration. The rim portion 7 of the disc can be furtherdivided into an upper (dead) rim portion R and a lower live rim portionR as shown in FIG. 5. The disc portions underlying the rim are the webportion W and the bore portion B. Each disc rim has lug portions 11. Aswill be noted from FIGS. 1 5, and 8(A), the upper portions U of theprior art disc rim lugs are of generally uniform. height (diameter) andcurvature in the outer rim periphery.

In contrast thereto, the discs of this invention have rims whose outerperiphery have raised (elevated) lug portions 13 adjacent to the slotsand lower intermediate rim portions 12 between raised portions 13.

As will be noted from FIG. 2, some turbine blades do not have aplatform. Instead, the disc rim cavities or lugs 9 receive the rootattachment in a position where the shank to root attachment transitionzone 4 lies closer to the upper portion of blades 1. As illustrated inFIG. 2, the zones of immediate stress-strain reaction are the blade rootattachment tang zones shown by cross-hatching at 10. Such stress-strainreaction zones 10 are shown on both the left and right hand sides of theroot attachment for blade 1 of FIG. 2.

FIGS. 3, 4(A) and 4(8) illustrate characteristic prior art blade rootand disc lug attachment configuration referred to in the art as aChristmas tree. In such blade root attachments, the blade rootattachment is defined by a plurality of blade tang portions 6 (FIG. 3),each such portion having mating lugs 11 (FIG. 4(A)) defining the slotportions 9 in the disc rim 7 which terminate upwardly at the outer rimperiphery in outermost portions U of uniform height (diameter) andcurvature in the outer rim periphery.

The disc rims of FIGS. 6 and 7, illustrating the present invention,characteristically show disc rim lugs 11 and corresponding disc rimslots 9 having both elevated, raised or extended portions 13 above thelower intermediate rim portions 12 (which are the adjacent and lowerlying portions of the disc rim periphery).

The elevated rim lug portions 13 provide increased restraint forreducing the bending deflections reacted as moments in the bladeshank/transition regions. Positioning of the extended disc rim lugs inclose proximity to the blade shank provides restraint of the shank whichlimits movement of the blade attachment tangs when centrifugal bodyforces load the blade attach ment tangs against the disc raised lugsportions 13 during rotation. This provides more uniform straindistribution for the attachment surfaces. The smoothly radiused raisedlug surfaces 13 of this invention tend to avoid stress/strainconcentrations on blade shank surfaces such as occur when the shankcomes in contact with the upper uniform surface portions U of the disclug 11 typical of FIGS. 1 3, 4(A), 4(3) and 5. The smoothly radiusedsurfaces provide, at a distance removed from the local origins of normalhigh strain intensity, non-linear contact surfaces that absorb bendinginduced contact pressure forces in a graduated manner. In accordancewith this invention, the uniform geometric contouring of the elevatedrim lug portions 13 is proportioned to accommodate the magnitude andrate of blade deflection during bending.

The net effect of the features of this invention is to reduce orsubstantially eliminate abrupt stress/strain transitions and loadnon-uniformities as compared with known art root attachments such asshown in FIGS. 1, 2, 3, 4(A), 4(8), and 5.

Prior art FIGS. I, 2, 3, 4(A), 4(8) and feature abrupt changes incontour in the disc rim lug portions 11 at upper portions U whichproduce localized Hertzian stress/strain concentrations when the sidesof the blade shank come in contact with the disc lug portions 11 whenbending of the blade occurs. Such concentrated stress/strain fields arenormally accommodated by the inherent ductility of conventionalmaterials such as steel, titanium and nickel-based, so-calledsuperalloys. Brittle materials such as ceramics and composites possesslimited ductility and must avoid such abrupt contour changes to preventstress concentrations from interacting. As shown in FIG. 2., there canexist a zone of comparatively severe stress-strain interaction in adeflected blade.

A further advantage of this invention resides in the fact that not onlymonolithic materials but also ceramics and composite material systemscan be utilized to make integral discs within the purview of thisinvention. Thus, materials such as composites and ceramics, whileusually classified as brittle because they possess little or noductility for redistributing local stress-strain concentrations, can beutilized in turbomachinery in-- corporating this invention.

The successful application of these materials to turbomachinery bladingdepends to a great extent upon the ability to avoid abrupt stress-strainconcentrations, e.g., as introduced by non-uniform loading. Conventionalmetals such as titanium tend to exhibit distress in blade rootattachments from local load nonuniformities. However, such distress canbe, and customarily is, manifested in the form of fretting wear, inducedfatigue or limited low cycle fatigue life as a consequence ofconcentrated high contact stresses.

Thus, the more gradual transition afforded by the present invention inthe blade attachment to shank transition region and the central shanksection of rotating turbine-compressor blading offers a more flexibleapproach to materials in the compressor blading art.

The restraining effect provided by this invention suppresses loadshifting from one blade root attachment to its opposing partner. Theelevated rim lug 11 can be in intimate contact with the blade shankportion prior to rotation or separated therefrom by a normal assemblytolerance gap.

FIGS. 9 and 10 depict characteristic prior art stressstrainrelationships vectorially and illustrate contrasts between disc rims ofFIGS. 1, 2 and 3. Such relationships can be compared with thosecharacteristic of this invention as illustrated by the diagrams of FIGS.11 and 12 with FIG. 11 referring to FIG. 6 and FIG. 12 illustrating thegeneral effect of FIG. 7s configuration on strain distribution.

FIG. 8(A) depicts one of the typical disc-to-blade root attachmentconfigurations known within the art in reference to FIGS. 1 and 2. FIG.9 illustrates the strain distribution existing on the outer portions ofthe blade attachment surfaces under uniformly loaded conditions for thesame configuration as FIG. 8(A).

As will be observed from FIGS. 9 12, a strain reversal occurs at theinitial point of contact of the disc rim lug (upper portion) with theblade attachment shank. The reversal occurs as the blade shank load istransferred to the root attachment tang. The outer surface straindistribution shown in FIGS. 9 12 is tensile as it approaches the contactpoint and it then converts to compression With the introduction ofnonuniform loads arising from centrifugal, centrifugal untwists,vibratory, gas bending, foreign object impact and others, one side oftheblade attachment is forced to absorb the loads relieved by its partner.The intensity of the strain reversal is illustrated in FIG. 10 andoccurs as a consequence of load redistribution in the form of bending.

FIG. 11 illustrates the effect of the configuration of FIG. 6 on loaddistribution. The magnitude of the stress reversal is reduced (ascompared with FIG. I as illustrated in FIG. 9) and taken up over agreater distance upwards along the shank surface.

FIG. 12 illustrates the effect of the configuration of FIG. 7 on loaddistribution. Similarly, the magnitude of the stress reversal is reduced(as compared with FIG. 2 as illustrated in FIG. 10) and is distributedover a significantly greater distance upwards along the blade shanksurface in like manner to that shown in FIG. II.

The present invention differs significantly from conventional prior artdisc rims which differ from one another based on metal characteristicswhich provide stress redistributing capability through inherentductility of the metal. This invention offers a distinct advantage offlexibility in choice of materials because these configurations avoidthe generation of strain gradients critical to material having lowductility such as composites and ceramics. The significance of this isthat the present invention permits the utilization of not onlymonolithic materials but also ceramics, and composite material systemsof ceramics and metals,-viz., ceramets in addition to the so-calledsuperalloys. Thus, the present invention can utilize such integral discmaterials as: monolithic material, such stainless steel; titanium alloyscustomarily usable at temperatures of 900F. to lOOOF.; nickel andcobalt-based so-called superalloys, viz., metal alloys containing nickeland/or cobalt and having a melting point range of approximately 2400F.to 2500F. and usable at temperatures up to 1800F.; ceramics stable attemperatures up to about 2500F.; fiber-reinforced metallic or inorganicand organic composite material systems, such as Boron/Aluminum,Graphite/Epoxy, Borsic Titanium etc. Other organic polymeric materialscan be used, e.g., silicone resins.

What is claimed is:

l. A turbine machinery disc having bore, web and rim portions, the rimportion of which is comprised of:

a plurality of circumferentially arranged symmetrical slots foraccommodating blades, each slot having blade tang-accommodating portionsof given radius of curvature;

a set of symmetrical rim lugs adjacent to each slot, each lug havingraised outer portions which are substantially of the same height andgradual radius of curvature, which radius of curvature exceeds that ofsaid blade-tang accommodating slot portions; and

lower symmetrical rim portions of approximately equal diameter betweensaid raised rim lugs;

said disc being further characterized as avoiding direct sharing oftension and compression between adjacent blades.

2. A turbine machinery disc as in claim 1 wherein said bore, web and rimportions are integral and comprised of ceramic material.

3. A turbine machinery disc as in claim 1 wherein said bore, web and rimportions are integral and comprised of ceramic and metal material.

4. A turbine machinery disc as in claim 1 wherein said bore, web and rimportions are integral and comprised of a metal alloy containing nickeland having a melting point ranging from approximately 2400F. to 2500F.

5. A turbine machinery disc as in claim ll wherein said bore, web andrim portions are integral and comprised of a metal alloy containingcobalt and having a melting point ranging from approximately 2400F. to2500F.

6. A turbine machinery disc as in claim 4 wherein said metal alloyincludes cobalt.

7. A turbine machinery disc as in claim 5 wherein said metal alloyincludes nickel.

8. A turbine machinery disc as in claim 1 wherein said bore, web and rimportions are integral and comprised of monolithic material.

9. A turbine machinery disc as in claim 1 wherein said bore, web and rimportions are integral and comprised of fiber-reinforced metalliccomposite material.

10. A turbine machinery disc as in claim 1 wherein said bore, web andrim portions are integral and comprised of fiber-reinforced organicpolymeric composite material.

11. A turbine machinery disc as in claim 1 wherein said bore, web andrim portions are integral and comprised of fiber-reinforced inorganiccomposite material.

1. A turbine machinery disc having bore, web and rim portions, the rim portion of which is comprised of: a plurality of circumferentially arranged symmetrical slots for accommodating blades, each slot having blade tang-accommodating portions of given radius of curvature; a set of symmetrical rim lugs adjacent to each slot, each lug having raised outer portions which are substantially of the same height and gradual radius of curvature, which radius of curvature exceeds that of said blade-tang accommodating slot portions; and lower symmetrical rim portions of approximately equal diameter between said raised rim lugs; said disc being further characterized as avoiding direct sharing of tension and compression between adjacent blades.
 2. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of ceramic material.
 3. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of ceramic and metal material.
 4. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of a metal alloy containing nickel and having a melting point ranging from approximately 2400*F. to 2500*F.
 5. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of a metal alloy containing cobalt and having a melting point ranging from approximately 2400*F. to 2500*F.
 6. A turbine machinery disc as in claim 4 wherein said metal alloy includes cobalt.
 7. A turbine machinery disc as in claim 5 wherein said metal alloy includes nickel.
 8. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of monolithic material.
 9. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced metallic composite material.
 10. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced organic polymeric composite material.
 11. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced inorganic composite material. 